The present invention relates to a measuring system in an annular slicing machine having an annular cutting blade, for detecting the cutting force exerted by said cutting blade onto a workpiece to be sliced during the cutting operation, the machine further having a mounting table, said workpiece being mounted on said mounting table displaceable in a direction transverse to the cutting direction, means for relative displacement of said mounting table and said cutting blade in the cutting direction for producing the cutting feed, and at least one measuring transducer for detecting the cutting force. Slicing machines of this kind are used for slicing brittle and hard materials such as semiconductor materials, for instance monocristalline silicon. They allow slicing with minimum cutting loss and at high precision regarding parallelity, evenness and thickness of the slices. However, in order to warrant such advantages a continuous supervision of the cutting process with a suitable and reliable measuring systems is required. As an example, it is usual to detect the deflection of the cutting blade from its plane and to take measures, particularly to tension and /or to dress the cutting blade if the detected deformation exceeds predetermined limit values (EP-A-0 139 067).
It is usual to measure the cutting force excerted by the cutting blade onto the workpiece to be sliced and to control the cutting feed and/or to dress the cutting blade in accordance with the measured value of the cutting force. U.S. Pat. No. 4,228,782 discloses systems for detecting the cutting force. In one of the disclosed embodiments the rod to be sliced together with a supporting bar is fixed with one end thereof in cantilever relation to a support. A measuring transducer is mounted between this fixed end of the rod and said support which is displaceable in the direction of the rod axis. In this case it is difficult to obtain sufficiently stable support of the workpiece. Since the distance of the cutting place from the measuring transducer decreases when succeeding cutting operations are carried out, new calibration of the measuring system would be necessary for each cutting operation, if strictly comparable conditions should be wanted for each cutting operation, this calibration taking into consideration the momentary distance between the cutting place and the transducer. For these reasons rods of limited lenght only may be sliced by means of this prior system.
With another embodiment disclosed in U.S. Pat. No. 4,228,782 the measuring transducer is located in the plane of the cutting blade and the supporting bar onto which the rod to be sliced is cemented directly rests and slides on the transducer. The accuracy of such a measurement strongly depends on how the rod end is clamped to its carrying block, and it is very difficult, to alway reproduce similar conditions. Therefore, a new calibration is required whenever a new rod to be sliced has been mounted. Moreover an accurate measurement of the cutting forces requires a very accurate parallelity of the bottom surface of the supporting bar resting on the transducer with the advancing or feeding direction of the workpiece, and also absolute evenness of this surface. Since it is hardly possible to meet with both conditions at the same time, large tolerances regarding parallelity and thickness of the slices will result. Subject to the flexibility of the clamping of the workpiece to its support, there always exist variable influences onto the results of the measurement of the cutting force.